In the search for improved sero-diagnostic tests, we have eliminated non-specific precipitins in E. histolytica antigen used in counter current immunoelectrophoresis with the barbital-borate buffer system. This was done by passing the antigen through a modified calcium phosphate column. Antigen which was only slightly reactive in the hemagglutination test was active in counter current electrophoresis. Soluble antigen has been prepared from Sarcocystis fusiformos zoites and has been successfully used to detect antibody to Sarcocystis in experimentally infected cattle.